I'm seeing lots of suggestions for Windows, but none for Mac. I'm using Acrobat 10.1.16 on an early 2009 iMac. Whenever I create a PDF I automatically do a "Save As" because it often reduces the file size. I would just re-save to the same folder and click "OK" when asked if I wanted to replace the existing file. Now -- and only about 70% of the time, and I can't figure out why -- I get this error message:

The file may be read-only, or another user may have it open. Please save the document with a different name or in a different folder.

The file isn't read-only; there are no other users; and the file isn't open anywhere else. I'm doing the same thing I've done thousands of times before. The only solution is to save it to another folder, and then re-save it to the original folder -- where it over-writes the original with no problem!

This only started when I upgraded to El Capitan. It's extremely annoying because this is something I do dozens of times a day. Kinda surprised that the problem has been known for over 6 months and Adobe hasn't provided a fix. Anyone?